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Daily Current Draw Calculator

The Daily Current Draw Calculator Calculation Sheet has intentionally been left unlocked in order that you may enter the current draw of each of the appliances on your boat, together with the daily periods that you have them turned on.

Current draw: The appliance amps currently entered on the sheet are notional. The most accurate way of establishing actual current draw on your boat is to turn off every source of current draw other than the one in question and refer to your battery monitor to see what current it is drawing. Otherwise refer to the manufacturer's data. It may be quoted in watts, which is volts x amps. Divide the wattage by voltage and you have the current draw.

Daily Use: Enter the hours of use for each of the appliances for when you are underway (day and/or night) and similarly for when you are at anchor. The yellow cells contain formulas which will calculate the amp-hours automatically.

The 'Total Requirement' will identify where you need the most battery juice - when you're underway or at anchor. Your house battery bank therefore needs to be sized based on that daily requirement.

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Yachting Monthly
Digital edition

How to improve power management on a yacht

August 21, 2024

Mike Morgan offers advice on how to improve power management on a yacht and preserve precious amps for those that like their home comforts

I confess, I’m not a marine electrician, and my understanding of boat electronics is at best rudimentary, but I’ve now been managing my boat’s power generation and consumption for three seasons and have developed an approach which seems to work well. Hopefully, you will find some of the following advice useful when it comes to managing your own yacht’s energy needs.

Every boat has its own particular balance of power generation and demand, so my system may not work perfectly for you, but it might help you start managing your precious amps a lot more effectively.

My wife Debbie and I sail up to nine months a year around the Med, predominantly lying at anchor. We avoid marinas and use our generator infrequently, to help save the planet and our budget.

I won’t address power needs whilst under sail here, as it’s not relevant to our cruising profile. Clearly, if you’re taking on an Atlantic crossing , then you’ll need to consider the power demands from your navigation equipment, lights and auto pilot.

We bought our pride and joy, Spirit, a Bavaria C57, brand new in 2021, and made several upgrades in an attempt to achieve the holy grail of self-sufficiency at anchor. We opted for 800 amp hours (Ah) hours provided by lithium batteries that weigh less than a single 150Ah lead acid battery.

Because lithium offers roughly twice the capacity of lead acid, that’s equivalent to 16 100Ah lead acid batteries with a combined weight of just over a third of a ton. Given Spirit’s generous beam, we’ve been able to accommodate four 420W solar panels, giving a potential maximum of 1,680W.

A few of the electrical galley appliances aboard Mike’s Bavaria C57 and the wattages that similar products might draw off your battery if you have an inverter

State of charge

The amount of electrical power you have available is all about batteries. Boat batteries are usually measured in amp hours (Ah) – the total number of amps devoured in one hour of use. So, a 120Ah battery will, theoretically, deliver 120A for one hour or 1A for 120 hours. But, of course, this is a little simplistic.

If you have lead acid batteries, you must never completely discharge them, unless you want to replace them regularly. Lead acid batteries should never be discharged below 50 per cent, so the practical Ah they really offer is half the theoretical Ah rating. In the above example, 60 hours at 1 amp would be the limit before you had to recharge the battery. Typically, the state of a battery’s charge is monitored by volts or a shunt battery monitor.

Knowing the state of charge of your batteries is critical to managing your power needs.

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I replaced our Bavaria’s standard 240Ah of domestic lead acid batteries with 800Ah of lithium batteries. The advantage of a lithium battery is its light weight. And, unlike a lead acid battery, it can be run down to a much lower charge. The downside is that lithium batteries have been known to explode.

To avoid this, they need to be paired with a battery management system, which is best left to a professional, who knows what they are doing, to install.

Oceanvolt lithium batteries aboard a Feeling 32

Charging sources

A standard ‘off the shelf’ mid-size production boat is likely to be fitted with a 60A battery charger which is used by the boat’s generator, if it has one, or when shore power is plugged in. The engine will also have an alternator which will typically produce between 35 and 60A of charge, depending on the size of the engine.

Assuming a 60A charge source, the batteries will receive 60A of charge in one hour. So, to put it very simplistically, if you have, as I do, 800Ah of lithium batteries and they are at 50 per cent, to charge them up to capacity would take 6.6 hours (400 amps divided by the charging source of 60 amps equals 6.6 hours).

Unfortunately, it’s not quite as simple as that. For example, there are various charging states – bulk, absorption and trickle (also known as maintenance or float) – and different types of batteries with different ratings, but I have kept it as simple as possible here for the purposes of explanation.

If you don’t have shore power (when at anchor, for instance), or don’t have a generator, the alternative is to run your engine for six hours under light load, which is not good for the engine and won’t win you many friends nearby who are trying to relax and enjoy a peaceful sundowner.

Mike’s customised electrical control panel

Battery charger

Increasing the size of your battery charger will speed up the process of charging from both a generator and shore power. I opted to fit a 120A charger and a 3kW inverter for my 240V appliances. There is always the option to beef up the engine alternator to feed a hungry family of batteries, but again, this means the boat engine needs to run for prolonged periods of time.

The 9kW Paguro 9000 generator I fitted produces a lot more power than we ever need. The generator powers both the 240V ‘ring main’ and the battery charger. However, the battery charging will be limited by the power rating of the charger, which in my case is 120A.

Four solar panels on Spirit’s stern arch produce a maximun 1,600W

Renewable energy

Renewable energy for boats is either wind, hydro or solar. I opted for solar on a custom-made stern arch. I fitted four 400W panels, which produce a theoretical maximum output of 1,600W at 12V or, in amp speak, 133A.

Like lithium batteries, the voltage and charge from solar panels needs to be managed, so each panel is equipped with an MPPT (maximum power point tracking) controller to ensure the batteries are getting the right amount of charge when the sun is shining. The next conundrum was to get all this in perfect balance based on the boat’s power consumption.

The stern arch was custom-built to support the solar panels

Background noise

I started by building a spreadsheet to calculate the various power ratings of my many onboard electrical appliances. However, this isn’t simple as you must calculate the power demand of each appliance, estimate how long you will run it for, and when you will run it.

You then need to map this over time to calculate a theoretical power demand and how much power you need to be generated. Estimating the power output from my solar panels alone became a headache: calculating the assumed number of ‘sunny’ daylight hours, the angle of the sun, solar panel efficiency, and when the next solar eclipse would be! So, like all people with limited brain capacity, I gave up.

I decided, instead, to take a more pragmatic approach. The first thing I did was to measure the ‘background noise’ of my boat; that is, the power being consumed whilst at anchor and not running any major appliances.

It turned out to be around 200A, which is very high; but then I do have three fridges, a deep freeze and more internal lighting than Blackpool Illuminations.

The time it takes to recharge my batteries once the sun has dragged itself up to the right angle differs dramatically based on which way the boat is lying. If my stern is exposed to the sunny side my batteries will fill to the brim in a few hours. However, if my bow is facing the sun, it takes a lot longer.

On an average day, we are at 100 per cent by midday or early afternoon, leaving a good four or five hours of surplus power generation for running more critical systems.

Air-con is a battery power ‘killer’

We have a lot of power consuming paraphernalia on board, for example the kettle, coffee maker, hair dryer, microwave oven, and so on, but I ignore these when it comes to power management as they are used randomly and are never on for long.

However, we do have several appliances that are critical to our power management, including a washing machine, water maker, ice maker and water heater. All of these have high demand and can run for long periods of time. I also have air-conditioning which can be run off the inverter, but I prefer to use fans and open hatches to keep the temperature tolerable when we are at anchor. Air-con is a battery power killer and is best left to when shore power is connected or the generator is running.

Our Bavaria came with a built-in utility room, so we decided to fit a full-sized washer-dryer, which has proven to be our favourite upgrade.

For this equipment I simply use a rota and allocate a specific day to run either water production, laundry, ice making or water heating. We do laundry once a week without using the drying function and relying instead on nature’s outside dryer, which does tend to lower the tone of an idyllic anchorage.

The water maker produces 60 litres an hour and I typically run it for around four hours, which will then keep us going for several days. I fit in ice-making and heating the water at other times.

Having guests on board who insist on having a shower every time they go for a dip off the swimming platform requires the water maker to be run most days. Inevitably under these circumstances I lose the battle of consumption versus generation and will need to resort to running the generator.

We chose a Schenker Smart 60-litre-per-hour, 12V water maker rated at 20A, which enables free freshwater production all day long thanks to Spirit’s cluster of four solar panels.

I always delay this until my battery charge is showing 30 per cent or less in the morning. At that point I will run the generator for three to four hours, which is enough to get my batteries back up to around 70-80 per cent, and then let the solar panels take over.

When I run the generator, I take advantage of the surplus power it produces by running as many devices as possible: I make water, run the air-con and heat water. Never waste any of those precious amps! I find that I run the generator, on average, every eight to 10 days when we’re on our own and every four to five days when we have guests.

Batteries can be easily distributed around a yacht

Before increasing the capacity of your service battery bank you need to calculate your total power requirement by multiplying the amperage of all the equipment by the period of time it will be run over a charge cycle (usually 24hrs).

Tally up the amp hours and then double the result (to allow for not going below 50 per cent of your charge capacity). Then add another 20 per cent to ensure you will always have enough to spare.

If you already have separate engine start and service batteries but want to add further service batteries, they should all be of the same age, type and capacity (Ah rating) to the first. It’s best to create your service bank from a number of smaller batteries and then link them together to achieve the total voltage and capacity you require.

If you’re planning to install a large bank (500Ah or more), it is often better to use 6V cells for this as these allow a large deep-cycling bank to be created, while still having the ability to move them around easily or distribute them evenly over a greater area.

Create an improved service bank by connecting a number of smaller batteries

Stay in charge

Once you’ve decided on the battery type, make sure you have enough charging power to fully charge them between cycles. As a rough guide you will need to be able to bulk-charge the bank at a minimum of 10 per cent of its rated capacity (ie. 20A for a 200Ah battery).

However, 20 per cent is a better figure to aim for if you’re looking to fully recharge over one night in a marina. Modern AGM (absorbent glass mat) style batteries can usually take a greater charge than wet lead-acid type, although gel cells require a more particular regime if they are not to be damaged.

Chargers (both mains and alternator regulators) should be of the multi-stage type, with bulk, absorb and float stages. This allows the batteries to be rapidly charged until they reach around 90 per cent charge, then the charge voltage drops to attain the final part of the charge more slowly, keeping temperature (and hence internal resistance) down, and eliminating gassing.

A smart battery monitor will allow you see your state of charge and remaining capacity

Temperature noticeably affects a battery’s ability to give out and absorb charge. The colder a battery gets, the greater the power required to charge it fully. For this reason, always fit a charger or regulator with a temperature sensor that will automatically compensate for these differences.

Most power devices produce a trickle charge, and are used to keep the engine battery topped up. However, if you’re planning to install a powerful (5A+) wind or water generator, or a large solar array, then you’ll need to install some sort of voltage regulator to prevent overcharging. This can vary, from a small solid-state switch for small solar panels, to a large dump resistor that dissipates excess charge from a wind generator through heating up a wire-wound resistor.

Monitoring your batteries

The easiest way to ensure your batteries are kept in tip-top condition is to observe their state of charge every day you’re on board, using a modern ‘smart’ battery monitor. This will give you a real-time display of the current going in and out, the state of charge (SOC), and the remaining capacity available. They also often have alarms to warn you when the voltage is dropping dangerously low, or if too high a charge is being applied.

A rough idea of the SOC can be attained using a voltmeter, but this is not particularly accurate and can indicate a false condition when recently charged or under a heavy load. It’s far better to install a monitor that has a shunt, which measures current flow over time and can calculate the available charge capacity remaining much more precisely.

Hydrogenerators, like this Remoran Wave 3, will quickly recharge a yacht’s batteries underway

Optimising solar power

The efficiency of solar panels can be compromised by saltwater and long-term exposure to UV and high temperatures. Good regular maintenance will improve a solar panel’s performance.

Clean your solar panels early in the morning, while they are at their coolest, as cleaning them when they are warm or exposed to direct sunlight can cause internal thermal stresses.

Use distilled or deionized water to avoid the formation of mineral stains or deposits on the surface of the panels, and avoid using harsh chemicals or abrasive solvents that could scratch the photovoltaic cells. Let the panels air-dry or use soft cloths, and make sure no water residue is left. Check regularly for cracks, breaks or loose connections.

Hydrogenerators

Hydrogeneration has become a great deal more efficient in recent years. It’s a very simple concept: the yacht’s motion through the water turns an alternator on the transom-mounted hydrogenerator which generates electricity to recharge the boat’s batteries. Achieving 300Ah each day is a realistic expectation when cruising at 7-8 knots.

Oceanvolt’s High Power ServoProp 25 electric saildrive

Main prop regeneration

You can also use your main propeller to ‘regenerate’ electricity whilst under sail by using a parallel hybrid propulsion system where an electric motor is installed alongside the engine. Lynch Motors in Devon has supplied its systems to Vendée Globe boats for years, purely as a re-generator, and now produces a Red Snapper electric motor for cruising yachts.

The only problem with a regeneration system is that the pitch required for the propeller to drive the boat efficiently through the water may not always be the same as the pitch for optimum regeneration. Manufacturers have tackled this in different ways.

Oceanvolt has developed its ServoProp for saildrives, which electronically adjusts its pitch depending on speed and function. The latest incarnation allows total 360° blade mobility and faces forwards, increasing efficiency: at six knots, it produces an eye-watering 1kW of power.

Bruntons has another solution with the cleverly engineered Autoprop, which automatically pitches up to match the boat speed. Its Ecostar version of the prop can generate 200W at five knots and up to 1kW at 10 knots when connected to an electric motor.

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How To Calculate Amp Usage Aboard a Boat

Almost every cruising boat, including us, seems to underestimate the amount of electricity we use per day when planning alternative energy – for us solar panels and wind generator. Very frustrating when your goal is to live by the sun and wind and not have to run the diesel or generator daily!

DISCLAIMER: I am NOT an electronics guru – I don’t really understand much of this stuff other than basic principles. What I DO know is that our alternative energy has NEVER kept up with our electrical consumption and this analysis shows why! 🙂 Keep in mind the power usage figures I’m using is what we’ve determined by using our Link 10 and turning things on & off to isolate individual items – not necessarily what’s quoted by the manufacturer. Hopefully, unlike us, you’ll figure out your alternative energy needs BEFORE you spend six years cruising frustrated every morning by the morning ritual of “how can we POSSIBLY be down that many amps!!!” 🙂

Before you can start to plan for a cruising vessel’s alternative energy plan, you need to know how many amp hours of electricity you use each day. Do you need to replace 100 amp hours … or 150 …. or 200 ??? Unfortunately there’s no shortcut easy way to calculate this information — I can’t tell you because it’s vastly different for every cruising boat. Even individual systems, such as radar, can consume vastly different amounts of juice based on how old they are (ours are ancient) and a variety of other factors, so there’s no one size fits all equation.

When we started outfitting Winterlude, we had a 55 amp alternator with our 30 hp diesel engine and that was it. No alternative energy at all. We didn’t pay as much attention as we should have to our alternative energy plan, and as a result, on an average we only replace about half of our daily usage via alternative energy. Entirely preventable if you plan correctly.

THE INVERTER FACTOR

HOWEVER, it’s not this simple — of course not! There’s nothing worse than running the noisy Honda 2000 generator before I even get my first cup of coffee! So, we use the inverter . Ours is modified sine wave and we’re lucky we’ve never had anything electronic break – a better choice for us would be pure sine wave, but it still works, so se la vie. Problem is, all inverters are different but ALL inverters waste power – it gets really really complicated to calculate how much wasted power there is in converting DC to AC so we use a “wasted” ratio of 2 to 1 — i.e. it takes twice as many DC amps to power that AC through the inverter. So for items powered via the inverter, I double the amps usage. I know this is not scientific, but it seems to come pretty close for our alternative energy calculations – if you’re more technical than I, feel free to jump in and let us know a better way to do this by leaving a comment below!

Here’s our at anchor list as a starting point, note that you need to know amps per hour AND an estimate of how many hours you use the item to calculate daily amp usage.

LED Anchor Light .25/hour X 10 hours = 2.5 amps/night

Adler Barber Cold Plate – Refrigerator & Freezer 6 amps/hour X 24 hours = 144 amps/day (theoretically it cycles on & off, which it does, but it still seems to take between 120 – 150 amps a day)

Bilge Pump: 3 amps/hour X 5 minutes + .25/day

Sensibulb LED Interior Lights: avg 3 lights on for 3 hours each = .20 amps/hour X 9 = 2 amps/day

VHF Radio: 6 amps transmit/ .5 amps receive – 12 hours = 6 amps + 10 minutes talk time = 1 amp = 7 amps total

SSB Radio: 1 hour receive @ 3 amps/10 minutes talk time @ 30 amps = 8 amps total

(NOTE: Both radios are different based on whether we’re using low power or high power, these are just guesstimate averages)

Coffee Pot: 6 cups of coffee – 3 amps each (including the inverter) = 18 amps

Cabin Fans: 2 amps/hour X 2 hours each or 4 hours = 8 amps (obviously if it’s hot and we run the pullman berth fan all night we use 20 amps, we probably need to replace these fans with more energy efficient fans, but they move SO much air!!)

Laptop Computer: 2 hours/day 5 amps/hour = 10 amps

Printer: 10 minutes/day at .35/hour

Charging Stuff (from phones to drills to handheld VHF’s etc): 5 amps/day average

So you can see with just the basic daily “stuff” we run, we average over 200 amps a day. Unfortunately, we only have 4 55 watt solar panels and a KISS Wind Generator. Figuring 14.5 amp hours from our solar (my simplified rule of thumb is 1 amp per every 15 watts) – and there are maybe 4 total hours when we generate max amps – so 14 amps X 4 hours = 56 amps, plus less for the remaining 5 hours or another 25 amps – total solar on a good day is 81 amps. Significantly short of our 200 amps/day usage. YIKES! Add wind — if it’s blowing 12 knots, we get maybe 3-4 amps/hour for a total of 72 amps a day – and rarely do we ever see this many amps in a day from the wind generator. Under perfect conditions, with our alternative energy choices, we would add 153 amps — and we’re using over 200. Bottom line is we can go about 3 days without having to use either our Honda 2000 portable generator or the diesel to recharge our 6 Trojan T105 wet cell batteries.

We didn’t do our homework well enough when equipping the boat for alternative energy! If we did it over again, we’d have at least 450 watts of solar – or 30 amps/hour from 450 watts or 120 amps from peak hours and another 55 from off peak hours = 174 amps on a good day for solar, plus the 72 from the wind generator for a total of 246 amp hours a day. Unfortunately perfect days are rare, but with 450 watts of solar and the wind generator, we should be able to keep up with our 200 amp daily usage.

Other stuff:

Spectra Catalina 300 Watermaker: 15 amps/hour, 13 gallons/hour takes 3-4 hours to fill one tank or 52+ amps – we usually run the Honda 2000 or make water underway. Technically we CAN make water using our alternative energy and sometimes do if the wind is blowing 15-18 and we’re generating significant wind amps as well as solar.

Don’t forget to calculate an under sail version of this same analysis – underway we run our navigation lights (since we’ve switched to LED, these are not a big draw, but before we switched they were HUGE – don’t leave them out of your analysis), our radar close to shipping lanes, our GPS – actually 2, a Garmin 541 at the helm and our laptop consistently for the Nobeltec electronic charts plus our Tridata Depth, Wind & Speed instruments. Update: if we were to do the electronics over again, we’d include AIS, so that’s another energy draw underway … who knows, we may add one soon anyway! 🙂

If we’re sailing these add up – especially the laptop with it’s 5 amps an hour draw = 120 per 24 hour period, plus another 7 per hour below = 288 amp hours in 24 hours NOT including the daily stuff such as the refrigerator…. YIKES! We limit the amount of time we need the laptop and radar actually running since we have a Garmin at the help and the radar only needs to be on if we’re dodging either ships or thunderstorms.

One last point …. we don’t include our electric windlass, electric autopilot or other items that are only used when the diesel is running because the alternator is charging and we’re not draining our batteries. If you use an electric autopilot underway when SAILING, not under power, then you’ll need to calculate the usage because they can be huge amp hogs & you don’t want to run your batteries down while enjoying your sail!

Please leave a comment and chime in to the discussion! THANKS! Jan

Baby, It’s COLD Inside! Keeping Warm on a Boat

Need More Fridge Space? Try a Portable Refrigerator/Freezer

13 Additions to Optimystique

19 comments.

Thank you very much for such an informative article, just at the right time for us. I was just about to post a question on this exact topic and this has given me enough to ponder over before I post a question.

My wife and I are currently selling up our home, motorhome and all our worldly possessions here in the UK in order to realise our dream of sailing the Caribbean and East Coast of the USA (Of course once we are more confident and proficient with the yacht we decide on and of course once we have plucked up the courage, we might do a “crossing of the pond”) lol.

Hi Len! I’m glad the post was helpful! Good luck with your lifestyle change — it’s amazing to be able to change your neighborhood and get involved with new cultures by merely raising the sails! Of course, you probably have somewhat of that with your motorhome, but we have no experience there! 🙂 Cheers! Jan

Jan – Thanks for taking the time and effort to put this information together. Extremely helpful! My wife and I were having our “alternative energy” conversation again last night. We will be interested to see the thoughts and input of others.

Len – We just finished eliminating all of our land-based life style “stuff” in July and are l Icing aboard full-time. The hassle is worth it. Good luck.

Thanks Dave! It’s such a complicated subject and I’m sure I don’t have all the details exact, BUT I do know every morning we grumble about not taking the time to determine we needed 450 amps of solar BEFORE we left the US! 🙂 Cheers! Jan

This is some really good information! Thanks for sharing your experiences. It’ll definitely come in handy when my wife and I start setting up our own boat.

Hi Jan, We are currently re-configuring our alternative energy sources and I found your article helpful! Quick question: How many charge controllers do you have on board? Do you have one for each solar panel?

Hi Michelle – we do not have a charge controller for each solar panel. They are configured together with a Solar Boost 2000E MPPT charge controller. It will take up to I think 350 watts and we currently have 225 in it. We’re seriously thinking about adding another 100 watts since we can configure them through the same controller. Good luck!

This site was… how do I say it? Relevant!! Finally I have found something which helped me. Thank you!

Keep this going please, great job!

There’s certainly a lot to know about this subject. I love all of the points you made.

Things are never as simple as they first seem. It looks like you’ve done a thorough job though. On the inverter, the manufacturer should be able to get you figures on expected output vs input. They don’t like to publish efficiencies probably because they would scare off customers. Going from lower voltage in to higher voltage out or from DC in to AC out will waste a lot of power. Sometimes you just have to do it though. The more power they waste, the hotter they run, just something to keep in mind.

Not sure if this thread is still active, but here goes;

Last month I was hit with this problem, fortunately it was only on an 100NM overnight trip (my 2nd ever, and mileage towards the next skipper level), but it got me thinking nonetheless. I’ve actually thought about it many times before, but only when I woke up just before dawn to no nav equipment or sailing lights, did I get the required motivation to investigate further. I run my yacht off a 12V system, so there is no inverter involved, but it also means that I have to run an extension lead whenever I plug into shore power and then connect a battery charger if I need to top up the batteries.

Hopefully I can get some further information, which may seem easy for you;

I have 2 battery banks, both made up from 12V 23Ah deep cycle batteries. The 1st is a single battery that I use to start the engine, the 2nd is 2 batteries in parallel which power the house. If I calculate the amp hour drain as you have described, how do I work out the life expectancy of my batteries? (I did notice that when I switched off the expensive nav light the drain dropped by about 4 amps on the meter!, then everything else just came back on).

The other thing is, how to I measure how much charge is coming from the alternative chargers, my solar panel for example?

This should be enough to get me started!

Thanks again for a very informative article, I also enjoyed the LED conversion article, I sound very much like David!

Hi Clive — if your batteries are 23 amp hours and there are 2 in parallel, it’s my understanding that you actually have a total of 46 amp hours in your house bank, but you can only effectively use 50%, so you’re back to 23 amp hours. If your nav light is pulling 4 amps, overnight for 8 hours, that’s 32 amp hours – exceeding your capacity. YIKES! We replaced our masthead nav light with an expensive LED. Like yours, ours pulled too much juice and it’s not something you can casually turn off during an overnight! Hope this helps. We can measure how much charge is coming in from our Solar Panels via the charge controller panel, but we have difficulty estimating how much is coming in from the wind generator since it’s just wired into the system. Our Link 10 doesn’t give us separate readings, so sometimes, we turn off EVERYTHING so there’s no charge coming out and look to see what the wind generator is putting in. Not science, but it gives us an idea. Not enough, I can tell you that! And keep in mind, solar is great, but there’s no solar charge offsetting anything overnight. 🙂 Cheers – Jan

Fantastic website. Just found it via wherethecoconutsgrow linked from a tiny house website. I’ve always been a water “rat” (windsurfing) and at some point in the future I want to downsize, take sailing lessons and buy a sailboat. Practical troubles for me are equipment storage (windsurf, paddle board, kayak, …) and power for electronics use; so your article sheds a little light on the puzzle, and that I better solar up big time 🙂

PS: you may need to curate some of the comments made that are very short & generic but have direct active (or now dead) links to commercial websites via the user name (url profile spam).

Thanks Frank! I try to catch all the spam comments, but sometimes a few slip through. My spam catcher catches over 2,500 a day so it’s not horrid, but it’s annoying just the same. I appreciate the input. And let me tell you, Peter & Jody on MaryChristine/Coconuts left with more toys that we have, which is amazing. Peter has several surfboard, their two Tower inflatable SUPS, fishing equipment, two large puppies and a dinghy. It’s possible … and FUN! Cheers! Jan

Hi Frank! Great post. I stumbled across this while trying to find energy consumption of our Garmin 541s.

Have been pondering the linklite battery monitor. Would you consider this essential, or just helpful?

Cheers, Don

Thanks for your sharing. Just bought a 36′ mainship, everything is new, lots of things to learn. Great help.

Congratulations Stephen! Friends of ours have a Mainship and are getting ready to “do the loop”. ENJOY! Jan

Calculating the Amp Usage Here are a few tips on how to count the amp usage on a boat, and you do not necessarily have to be an engineer or very adept in electronics to be able to do so. First, you have to know how many amps are being consumed daily. You have to be very alert and count all the amps that are being used on board. The computation for amps and voltage, if you are not aware, is Watts / voltage = AMPs. For example, you use 1425 watts in 120 volts, then it lookst like 1425 / 120 ~ approximately 12 AMPs. Make sure you are able to go through this in details with all electronics on board, such as the LED lights, on board and on the anchor, VHF radio, cold plates used in the refrigerator and freezer. Coffee pot, electronic fan, and so on. This will be in so much detail, but the more you work on it, the more accurate your computation will be.

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Jeanneau Model: SO 39i
Yacht Name: Be Cool
Home Port: San Carles
Country: Spain

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I have developed a spread sheet to calculate the power consumption of my Jeanneau 39i whilst cruising the med underway and at anchor. I built it to estimate how often I would need to run my generator. Fairly rough guide but might be useful.

If anyone wants a copy please send me a message with you email address and I will forward.

Jeanneau Guru Yacht Name: War Machine Home Port: Melbourne Country: Australia	Select Post Deselect Post Link to Post Member Give Gift Back to Top

Jeanneau Guru	Select Post Deselect Post Link to Post Member Give Gift Back to Top

Expert Member Yacht Name: Mistroma of Gair Home Port: Variable, currently in Ionian Country: Boat in Greece.	Select Post Deselect Post Link to Post Member Give Gift Back to Top
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New Member

Jeanneau Model: SO 39i
Yacht Name: Be Cool
Home Port: San Carles
Country: Spain

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What I am trying to do is make the boat as independent as possible for longer passages. However, my initial cruising is going to be around the western med islands so will always have access to fuel pontoons to fill the water tanks.

I have 3 domestic 110amp batteries so another option is to install more but space is limited.

I bought the boat with very little on board and had a limited budget of £10K to upgrade her. Managed all the above fitted and a lot more (have list if interested) with change!

She is now a well sorted boat with all options ticked and requires nothing else. Been an interesting project.

Planning first adventure sailing from Sant Carles to the Balearics for 5 weeks at the end of the month with wife, two daughters and a friend. Going to be cosy!

Haddock

Full Member New Member Jeanneau Model: SO 39i Yacht Name: Be Cool Home Port: San Carles Country: Spain	Select Post Deselect Post Link to Post Member Give Gift Back to Top Thanks Mike

Full Member New Member Jeanneau Model: SO 39i Yacht Name: Be Cool Home Port: San Carles Country: Spain	Select Post Deselect Post Link to Post Member Give Gift Back to Top I will be leaving Sant Carles on the 29th of June then heading south to the Columbretes and on to Ibiza so unlikely to hook up. Great anchorage in the bay if you have not been there before, very protected. Look forward to receiving the numbers. Enjoy your sail! Haddock

Expert Member

Yacht Name: Mistroma of Gair
Home Port: Variable, currently in Ionian
Country: Boat in Greece.

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I realised that the raw data was probably not much use and added some extra information. I tended to aggregate days in a marina but usually kept a log for each day when at anchor. Batteries were always on mains charger in a marina and so I wasn't bothered much with the detail.

Filter by "Anchorage" in first column to get off-grid readings
Last 4 columns are Net Total, Net, Solar and Wind Gen

Net Total is output from panels and wind gen going into batteries
Net is simply solar and wind added together

Net total to batteries will be lower that Net figure as the regulator throws away power whenever batteries are well charged.

I also have data for 2012-2014 from France, Spain & Portugal but will need to tidy it up.

Full Member New Member Jeanneau Model: SO 39i Yacht Name: Be Cool Home Port: San Carles Country: Spain	Select Post Deselect Post Link to Post Member Give Gift Back to Top Ta Mike

Senior Member A power boater thinks they are going somewhere special; a sailor is already there. Jeanneau Model: SO 37 Yacht Name: Sunniva Home Port: Salem, MA Country: USA	Select Post Deselect Post Link to Post Member Give Gift Back to Top

Simple Guide for Calculating Your Sailboat’s Energy Budget

A helpful approach to calculating your solar and battery systems for your sailboat or RV.

Post author By Ryan
Post date December 22, 2020
3 Comments on Simple Guide for Calculating Your Sailboat’s Energy Budget

After spending way too much time figuring out how to size the power system for our boat, I thought it would be good to create a simple guide to estimating your needs. It is an excel file you can download/modify with your own sailing or RV needs. I ran through this math with our teardrop trailer, and now with the more complicated sailboat. This whole file is set up for a 12-volt system, you may need to make some modifications to this file for different voltages.

Start at the top of the document and fill out the yellow boxes. The file The results will show up at the bottom.

Energy Calculator

Think of your system as the combination of three different calculations:

Energy generation from solar, wind turbine, generator, and/or alternator
Energy storage to/from the battery bank
Energy draw to the system demands

Each system needs to be sized appropriately for your application, which starts with the demand you expect to have in your system. Start by listing all of the loads that will be on your system, and classify them in different ways: on anchor vs. on passage and define the minimum critical requirements. Then figure out how many amps and how many hours each draw will take on a given day – either on passage or at anchor. For example, we don’t need to run our autopilot while at anchor, and it’s one of the biggest amp draws we have on our boat.

Once you understand your overall system needs, you can play with sizing your solar panels and battery bank. This is the generation side of the equation. You want to make sure you’re accounting for usable sunlight, clouds, and a safety factor when making your assumptions. You also want to make sure you’ve got the ability to weather a few days of low (or zero) power generation. This all gets calculated at the bottom of the excel file where it shows the final calculations of how long you’d be able to last (theoretically) in each scenario, and what your excess/deficit would be.

What do you think? I’d love to get some feedback on the file/calculations.

Tags amp draw sailboat , autopilot , Battle Born Batteries , Battle born lithium sailboat , current draw sailing autopilot , energy demands sailboat , sailboat energy budget , sailboat power calculator , sailboat solar , Sailing , sailing current draw , sizing battery bank sailboat , Sizing solar boat , solar power calculator , solar powered sailboat

3 replies on “Simple Guide for Calculating Your Sailboat’s Energy Budget”

Hey guys , lovely to read your blog regarding your ericson. I too own a 39b here in New Zealand and slowly going through a Refit. My understanding is only 19 to 20 of these were built. yours looks in great condition. regards Kyle

Thanks for the comment! Great to hear about other 39B’s out there! Overall it is in great condition, however we do have some wet spots we’re currently re-coring in the cockpit & foredeck. We’d like to hear more about your refit – we’re pretty active on Instagram @gerbersunderway if you want to message us there

Only just noticed your reply, sorry we don’t have Instagram but will try looking you up. regards Kyle

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26-04-2006, 08:19
Boat: Boatless, for now, Cat enthusiast	so I can best spec out bank requirements, generation, etc. While underway, the will obviously be a significant consumer. It will vary according to a number of factors (sea state, balance of , etc.) and I understand that. I've looked on the manufacturer's spec (Raymarine ST6001) and not seeing much help. The figures they supply lead to a calculation of up to 360 amphrs/day. I've got to have that wrong, surely, or lots of wouldn't be getting very far with that sort of and the bank required to feed it would sink the bloody boat! So, any guidance on this? I understand that the range of daily may be pretty wide, but what is a reasonable figure to use for the ? Thank you. ID Observations are gold; hypotheses, silver; and conclusions, bronze. Democracy is two wolves and a lamb voting on what to have for lunch. Liberty is a well-armed lamb contesting the vote.--Ben Franklin Everyone is entitled to their own opinion, but not their own facts.--Daniel Patrick Moynihan

26-04-2006, 08:51
Boat: (Cruiser Living On Dirt)

26-04-2006, 09:20
Boat: Viking 33 Tanzer 8.5m Tanzer 22	and the sea conditions. Last first. If the conditions are bouncing the boat around and making it alter course the AP unit will run more often, if the boat is not balanced the AP will run more often, and if the AP is a seeker it will run more often. The last part might be critical and all the new units may be seekers. By that I mean they do not go to sleep, they are always checking where they are going to make sure they are on course. A non seeker goes to sleep while on course and only wakes up when the boat goes off course. A seeker may be consuming all the time, and more power when it makes a course correction. So as long as the boat is on course and the boat is balanced and the sea state is steady, the non seeker AP may use zero amps. That is the case with Ethel my old Tiller Master. Ethel however is slow when she wakes up which is fine for a balanced boat, but some may require more immeadiate action. Ultimately I think I will use Ethel while under power, and a while sailing. Michael

26-04-2006, 09:41
Boat: Boatless, for now, Cat enthusiast	, the first one hasn't hit the yet so we have no empirical data regarding how the boat will behave. I'm assuming, though, that with sufficient care, it will be possible to reasonably balance the weight distribution of the boat and sail trim will, of course, be dependent on conditions. As part of specing out the boat, I'm being asked about the size of the bank to install. So, I've put together an Excel sheet to do some projections and estimations. Assuming that under passage-making conditions, the will be running 24/7, how much battery capacity should be budgeted? I understand that the actual power used will be a range that will vary by conditions, but is there some sort of average, perhaps with a standard deviation, that could be used for the budget? Thanks. ID Observations are gold; hypotheses, silver; and conclusions, bronze. Democracy is two wolves and a lamb voting on what to have for lunch. Liberty is a well-armed lamb contesting the vote.--Ben Franklin Everyone is entitled to their own opinion, but not their own facts.--Daniel Patrick Moynihan

26-04-2006, 09:51
Boat: Privilege 37	pilot power consumption has two elements - continuous (milliamps) to power the brain, and and a Much higherconsumption for the bit that actually turns the . I suspect your calculations have been based on the power requirements for the latter. The number quoted is the maximum needed to provide maximum turning capability, and is likely to be very different from what is actually required. A does not need anywhere near as much power to turn the rudders as a mono. Balance of the will make a huge difference in power consumption, the is unlikely to be moving all the time (especially if you have balanced the properly). If you have purchased the rate gyro system, rudder movements will be made almost in anticipation of requirement, thus much less than if left later. If your rudders are balanced at all, this will also reduce the power requirement. It is one of the largest power requirements (with the Fridge and freezers) but should be manageable. The highest consumption rudder is the unit, designed for use with wire systems, whereas the hydraulic system should be less.

26-04-2006, 11:11
Boat: Boatless, for now, Cat enthusiast	and over a 24 hr period. If that is .2, then over 24 hours that will equal 4.8. When it decides it actually needs to move the rudder, then it will consume the higher figure -- say, 15 amps -- but only for the time actually moving the rudder. The sum of time actually spent moving the rudder with a balanced boat in steady winds may only be minutes in a day. For sake of illustration, let's say 60. Then, the total power consumed over the course of the day will be 4.8 + 15 = 19.8 amphrs. Do I have that right? Still not a trivial amount, but a lot less than I what I originally was computing. Thanks. ID Observations are gold; hypotheses, silver; and conclusions, bronze. Democracy is two wolves and a lamb voting on what to have for lunch. Liberty is a well-armed lamb contesting the vote.--Ben Franklin Everyone is entitled to their own opinion, but not their own facts.--Daniel Patrick Moynihan

26-04-2006, 11:19
Boat: Privilege 37	correctly, I estimated out a similar system at abt 50 amp/hrs/day.

26-04-2006, 12:07
Boat: C&C Landfall 39 center cockpit "Anahita"	do you have? The non-hydraulic units are not as efficient, especially if you have to back-drive the friction of cable steering. I had a 300 Watt hydraulic drive unit which pushed 200 Amp-hours for 24 hours in a and only 20 Amp-hours in mild stuff. In this case it is easier to figure an average power consumption equal to half the peak power rating of the drive for the 24 hour calculation for a "bad case" of power consumption. You will then be well under 360 Amp-hours for 24 hours.

26-04-2006, 12:13
Boat: Sceptre 41

26-04-2006, 12:14
	strategies, which of course, you already know. The Devil is in the details… Good luck. Catalina 34 MkII G. K. Chesterfield

26-04-2006, 16:46
	[type 2 L] which is driven by -- I would estimate at least 65-70 AHrs/day based on 24x7. This assumes a relatively balanced boat in normal conditions - i.e not flat but not heavy . This might be a little high or low but will put you in the range I believe. We sized our bank assuming 100 /ahrs day for autopilot. Unfortunately can't measure as standalone as we have other systems running all the time so can't break it out. But we avg around 225 Ahrs day total consumption including : , autopilot, stereo, lights [house/nav], computer, instruments, as needed, etc.

26-04-2006, 18:44
Boat: C&C Landfall 39 center cockpit "Anahita"	divided by time whereas Amp-hours is multiplied by time which, then, is only missing the voltage multiplier (often assumed to be a nominal 12V or whatever is the case) to get true energy consumption, what you pay for when you pay your electricity bill. No one has ever been billed for Amp-hour consumption.

26-04-2006, 19:54
Boat: Sceptre 41

27-04-2006, 09:36
Boat: C&C Landfall 39 center cockpit "Anahita"

11-06-2006, 17:03
Boat: 1980 Endeavour 43 (Ketch)	, rudder , and two control heads. I also run an anemometer, , speed , and four display heads (all RayMarine). The is a VERY old Ratheon unit (25 plus years), and doesn't play with others. I am VERY happy with the Autopilot system. It is difficult to judge the amount of current drawn by the autopilot system. In standby (which I think would be indicative of power consumption when not actively controling the rudder), my system (without radar or , but with my VHF) drawns what appears to be less than one amp. When the autopilot is engaged and steering in light to moderate seas and winds (<6' and <20kn) with a reasonably ballanced sail plan it hardly seems to draw much more than 2 amps for a very short period of time (NOT continuous). And, damn it, it steers a much better course than I do. grrrrrrrr

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Sailo's Boat Calculator

The Sailo Boat Calculator is a tool that allows you to explore, predict, and plan costs and revenues associated to boat ownership. The most important user inputs can be found on the left side of the Cost of Ownership tab. The calculator has built-in models that compute costs as a function of the information provided.

The calculator is organized in multiple tabs that show costs breakdown and allow for detailed customization. For example, the fuel cost tab computes fuel consumption based on the type and size of your boat, estimated HP, and average current gas prices. To make this calculation more accurate you can enter a more exact fuel consumption for your boat and more accurate local gas prices.

The last two tabs are probably the most interesting. The Charter Profit section estimates the income your boat can generate on a platform like Sailo based on charter rates and days rented. Of course we increase maintenance costs due to chartering based on the number of extra days on the water. The Rent vs Buy tab shows a comparison between renting and owning an identical boat to find which option is the most economical and by how much. Note: we assume identical fuel consumption and cost for both rental and personal use. Read more about it here .

COST OF OWNERSHIP Click tabs below to see costs breakdown
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Renting vs owning (per year), calculator feedback, sailo boat ownership calculator, thank you for taking time to give us feedback. you feedback is important in improving the accuracy of the calculator results., the results for my boat were reasonable, ease of use, the calculator is easy to use and understand, the calculator design is clean and appealing, the calculator is useful.

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Boat Speed Calculator

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The boat speed calculator determines the top speed of a boat based on the boat's power and displacement . If you wonder how fast a boat can go, this calculator will help you answer that. The calculator also utilizes a constant known as Crouch constant which differs based on the type of the boat.

The formula for the top speed of a boat is used by designers to perform preliminary design analysis of the hulls. This helps in keeping the cost of building a boat in check (visit the boat loan calculator for more). Read on to understand how to calculate the speed of your yacht using Crouch's formula and to know how much horsepower do I need for my boat?

What is boat speed — Calculating using Crouch's formula?

The speed of the boat, in simple words, is how fast it can go. However, unlike land vehicles, this speed is not a ratio of distance and time. The speed of a boat having an engine to deliver P horsepower and displacing D pounds is written as:

where S is the boat speed and C is the Crouch constant. The above equation is known as Crouch's formula.

Note: The formulation and value for the Crouch constant are specific for units such as the speed in miles per hour and displacement in pounds.

💡 Our tools can convert units automatically, but if you'd like to learn how to do these conversions yourself, then our speed conversion and torque to hp calculator could come in handy!

What is displacement?

The displacement for a boat is defined as the volume of water displaced . The volume is then converted to weight. This property of a ship is an application of Archimedes' principle . In other words, the displacement of a boat is its weight. This weight is usually measured in tonnes or pounds. For instance, a modern US Navy Gerald R. Ford-class aircraft carrier displaces about 100,000 tons at its full load, whereas a 17th-century fishing boat displaces only about 13 tons. The tonnage of the ship varies as per its class and purpose.

Keep reading about Archimedes' principle at our Archimedes' principle calculator and find out if an object sinks or floats in a liquid!

Crouch constant

The Crouch constant depends on the type of boat . The constant is applicable to a wide variety of boats, from runabouts to high-speed racing boats. It does not take the hull length into account. The table below has the value of the Crouch constant for different types.

Constant	Boat types
150	Cruisers, average runabouts, passenger vessels
190	Light high-speed cruisers, High-speed runabouts
210	Racing boats
220	Hydroplanes
230	Racing catamarans, Sea sleds

How to calculate boat speed using this calculator?

Follow the steps below to calculate boat speed:

Step 1: Enter the shaft horsepower value, P .

Step 2: Insert the boat's displacement , D .

Step 3: Choose the Crouch constant , C from the list of boat types , or you can directly enter the value.

Step 4: The boat speed calculator will now return the value of boat's top speed.

Example of using the boat speed calculator

Calculate the speed of a racing hydroplane having an engine that delivers 3000 hp and displaces 6800 pounds of water.

To calculate boat speed :

Step 1: Enter shaft horsepower value P = 3000 hp .

Step 2: Insert the boat's displacement , D = 6800 lbs .

Step 3: Choose the Crouch constant , C from the list for hydroplanes, i.e., C = 220 .

Step 4: Using the Crouch's formula: S = √(P / D) × C = √(3000 / 6800) × 220 = 146.13 mph i.e., the speed of the hydroplane is about 146.13 miles per hour.

Alternatively, you can also run this calculator backward to know how much horsepower I need for my boat to achieve a certain speed. Say you want a top speed of 150 miles per hour for your 6,000 lb hydroplane. You can then:

Step 1: Enter top speed value S = 150 mph .

Step 2: Insert the boat's displacement , D = 6000 lbs .

Step 4: The calculator will use Crouch's formula to return the horsepower value as: Power = (P / C)² × D = (150 / 220)² × 6000 = 2789 hp

Therefore, you need an engine to deliver about 2800 hp to take your boat as fast as 150 mph .

How do I calculate a boat's top speed?

To calculate the boat speed:

Divide the power delivered by the boat to the displacement.

Find the square root of the result from step 1.

Multiply by the Crouch constant.

S = √(P / D) × C

What is Crouch's formula?

Crouch's formula is the equation to find the top speed of a boat based on its power P and tonnage D . The speed of the boat, S is given by the equation.

What is the value of Crouch's constant for a racing boat?

A racing boat has the value of Crouch constant around 210 .

What is the value of Crouch's constant for runabout boats?

An average runabout has the value of Crouch constant around 150 whereas it can go up to 190 for high-speed runabouts .

Shaft horsepower (P)

Boat displacement (D)

Crouch's constant (C)

Welcome to the West Nautical Fuel Calculator

HOW TO USE:

To plot points on the map, click with your mouse - this will automatically update the distance table. Then enter the speed, fuel consumption, and fuel cost to determine the total cost of the trip.

Example 1: A fast 30m yacht cruising at 20 knots ( Lady Amanda ) will consume roughly 400-500 l/hour (more depending on engine type).

Exampe 2: A typical displacement yacht may cruise at 12 knots and consume 300 l/hour

Example 3: Some yachts can cruise at 10 knots ( Firefly ) and consume 100 l/hour

Example 4: A sailing catamaran can cruise at 8 knots and consume around 35 l/hour

Fuel prices can fluctuate, but typically fuel is between €0.8 - €2.2 per litre.

Get in touch with one of our client managers for a more accurate fuel distance calculation.

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How Much Horsepower Do I Need for My Boat?

If you’ve been searching for a boat to purchase, or have reached the point at which you’d like to get a new engine, chances are you’ve asked the question, “How much horsepower do I need for my boat?” While the individual concerns may be different — wanting to make sure there’s enough horsepower or not too much horsepower — it’s a question many people who are interested in purchasing a new boat ask.

Sometimes, the follow-up question is, “Is it illegal to overpower a boat?” Whether you’ve been asking yourself one of these questions, or are just curious about how horsepower can affect the cost of fuel and insurance, we’ve gathered several pieces of information to educate you on horsepower. Through reading this information, you’ll be able to learn more about where it came from, how it’s calculated, how to determine the amount you need and the dangers that come with having too much.

What Is Boat Horsepower?

Horsepower is defined as a unit of power equal to 550 foot-pounds per second used to measure the power of an engine. Today, it applies to boat and auto engines, but its original use was to describe the power of a steam engine. In the late 1700s, a Scottish engineer named James Watt invented the first steam engine, which improved on a design pioneered by Thomas Newcomen in 1712 . It was a big deal. This new steam engine could do the same amount of work as the former Newcomen engine, but used only one-quarter of the fuel.

Unfortunately, comparing the steam engine to the Newcomen engine wasn’t effective marketing, as most of the population was still using horses for mechanical work. To market his new product to this audience, Watt knew he had to come up with a way to compare the work of horses to the work of his invention. Through his experiments, he determined one horse could do about 33,000 foot-pounds of work in one minute — meaning a horse could lift a 33,000-pound weight one foot in one minute. Therefore, he defined one horsepower as 33,000 foot-pounds of work per minute — or 550 foot-pounds per second.

There were a few flaws with this new measurement — the biggest being the assumption that a horse could continue to work at that consistent rate instead of tiring out. However, Watt didn’t let that fact bother him, and it didn’t bother his customers, either. Comparing the power of a horse to the power of a steam engine showed Watt’s steam engine could do the work of five horses, and it went on to become an integral part of the Industrial Revolution.

How Is Boat Horsepower Calculated?

The relevance of horsepower, the measurement of 550 foot-pounds per second, didn’t stop with the Industrial Revolution. The measurement of horsepower was converted into other units of measurement. For example, other experiments determined one horsepower equals 746 watts of energy. In other words, if you put a one-horsepower horse on a treadmill, it would be able to operate a generator producing 746 watts. Engineers also did calculations to relate horsepower to torque, which is especially important for boat engines.

Torque is easiest to explain through an example. Imagine you have a large socket wrench with a two-foot handle. You apply 50 pounds of force to that handle — when you do that, you’re applying a torque or turning force of a total of 100 pound-feet to the bold. Keep in mind, with that calculation, you could get the same result — 100 pound-feet of torque — by applying one pound of force to a socket wrench with a 100-foot handle, or by applying 100 pounds of force to a socket wrench with a one-foot handle.

In an engine, torque produces power — so being able to relate it to horsepower is critical. A device called a dynamometer applies a load on the engine and then measures the amount of power it produces to determine torque. Marine dynamometers are available, too — taking into consideration boat operation by simulating on-the-water operation. Once the torque has been determined, you’re able to convert torque to horsepower by multiplying torque by revolutions per minute (rpm) and dividing that product by 5,252. The divisor, 5,252, comes from a series of calculations that convert rpm to radians per second.

Through using a dynamometer, you’ll be able to see the horsepower versus rpm values for the engine, which is especially important for calculating peak horsepower. Engines will have a point in rpm at which the power available from the engine has reached its maximum. This is known as peak horsepower — it’s often documented as “___ HP at ____ rpm.”

Determining How Much Horsepower You Need

Once you understand the history of horsepower and how that’s connected to the calculation we use today, it’s natural to wonder how much horsepower your boat needs. There are several factors to take into consideration when you’re determining how much horsepower you need — the manufacturer’s limits and recommendations, boat horsepower-to-weight ratio, fuel efficiency, use of the boat, number of people on the boat and an industry rule of thumb. Here are some things to consider in each of these areas to help you answer the question, “How much horsepower do I need for my boat?”

How Much Horsepower Do I Need For My Boat V2 01 1

Manufacturer Limits

The easiest place to start is with the boat’s capacity plate — or owner’s manual. In addition to giving you a maximum for passengers and cargo, the manufacturer will also spell out the absolute maximum boat horsepower. If you have a boat that was built before 1972, came from overseas or was home-built, you may not have a capacity plate, but boat owner’s manuals are often available online. If not, you can always contact the boat’s manufacturer to inquire about their limits and recommendations for your particular boat model .

Boat Horsepower-to-Weight Ratio

When you’re trying to determine the amount of horsepower you need, it’s essential to consider the weight of the boat. The boat horsepower-to-weight ratio is simple to calculate and can be expressed in horsepower per pound or pounds per horsepower.

Let’s say, for example, your boat weighs 5,000 pounds, and it has a 300-horsepower engine. Taking 5,000 divided by 300 gives you a result of 16.6 pounds per horsepower. Doing the opposite calculation — taking 300 divided by 5,000 — gives you a result of 0.06 horsepower per pound. The lower the number, the faster your boat will go. Remember the boat horsepower-to-weight ratio once you’ve decided on horsepower and are matching outboard to boat size. While one or two outboards may give you the same horsepower result, keep in mind additional weight will accompany each additional outboard motor.

Fuel Efficiency

The amount of horsepower you choose will impact your fuel efficiency. However, just because you have a higher-horsepower engine does not necessarily mean you’re going to use more fuel. According to Boating magazine , running your gas engine between 3,000 and 3,500 rpm and your diesel engine at three-quarters throttle is the sweet spot for fuel efficiency. If you’re running a lower horsepower engine at full throttle all the time, it’s going to use more gas than a higher horsepower with less throttle. Keep this fact in mind as you consider what horsepower to choose.

For those who prefer exact calculations, Boating magazine has provided some calculations you can use to run some of the numbers. You’ll be calculating the gallons of fuel that are burned per hour (GPH). To do this, you need to know gasoline weighs approximately 6.1 pounds per gallon, while diesel weighs about 7.2 pounds per gallon. You also need to know a well maintained four-stroke gasoline engine is estimated to burn about 0.5 pounds of fuel per horsepower per hour, while a similar diesel engine is estimated to burn 0.4 pounds of fuel per hour.

The equation is GPH = (specific fuel consumption x HP)/fuel specific weight. For example, if you want to determine the fuel consumption for a 300-horsepower gasoline engine, you would calculate (0.50 x 300)/ 6.1, giving you a result of 24.5 gallons per hour.

As with most decisions related to boating, the use of the boat is always a factor. Are you using the boat just to cruise with friends and family ? Or will you be pulling water skiers, wakeboarders and tubers ? The addition of pulling someone behind the boat — and the additional weight of storing watersport accessories — increase the need for power and are often a reason to consider adding horsepower to your boat.

Number of People

Once you’ve considered the use of your boat, the next question to ask is what the normal number of passengers for your boat will be. If it’s usually just you and a friend or a spouse, that weight is different than if you enjoy boating with several of your family members and friends.

Rule of Thumb

If you’re the type of person who doesn’t need precise calculations — or just doesn’t want to be bothered with them — the Boat Trader blog offers a rule of thumb to use when determining the amount of horsepower for your boat. The rule of thumb is based on weight alone, and says you should have between 40 and 25 pounds of weight for each horsepower.

For example, a 5,000-pound boat could have an engine with between 125 and 200 horsepower. Yes, the range is wide, but that’s because boats have a variety of different designs and handle differently. While this rule of thumb can be a helpful way to get a ballpark range, it still requires some guesswork when it comes to considering your boat handling.

Federal Regulations

Is it illegal to overpower a boat? According to the federal government, yes. There are a few different ways you can define overpowering a boat. The horsepower capacity section of the Code of Federal Regulations contains its definition of overpowering a boat.

There are two different ways the federal government uses to determine the maximum horsepower for any given boat — one is a computation, and the other is a performance test. The way that is used depends on the boat. For the majority, the computation method is best to use. You multiply your boat length by the transom width. Then you take that number, which is known as the “factor,” and match it to a horsepower capacity according to the Code of Federal Regulations Table 183.53 — Outboard Boat Horsepower Capacity, shown below.

Don’t forget to adjust the result based on remote steering, transom height and boat bottom.

Determine The Maximum Horsepower Image 1

The performance test method is for boats that are 13 feet or less in length, have remote wheel steering, have a maximum capacity of no more than two persons and at least a 19-inch transom height — or at least a 19-inch motorwell height and at least a 15-inch transom height. Through this method, there are very specific instructions for boat preparation addressing everything from motor mounting to fuel tanks to ensure consistency. There are equally as specific instructions for the conditions in which you can perform this test.

The first part of the performance test is the quick-turn test. Setting the throttle at a low maneuvering speed and facing straight ahead, you then turn the wheel 180 degrees in half a second or less and hold it there. If you can complete the 90-degree turn without losing control of the boat or reducing the throttle, your boat has passed the test. Repeat, increasing the turn in speed until you can no longer pass the test, or you reach the maximum throttle. The maximum horsepower the boat can use while still completing this test is defined as the maximum horsepower capacity, unless it is more than 40 horsepower, in which case, the maximum horsepower capacity is capped at 40.

The good news is, these rules are in place for boat manufacturers, so assuming your boat’s manufacturer is following the federal regulations, you can consider the maximum horsepower capacity listed on your boat meets the federal regulation for its maximum horsepower.

Insurance Considerations

The amount of horsepower your boat has will influence your boat insurance, which is another fact to consider. There are three main areas of insurance the amount of horsepower you choose for your boat will affect — overall coverage, premium cost and type of policy.

Overall Coverage

There is also a chance your insurance company will not cover a vessel that exceeds the boat manufacturer’s max horsepower. This is an extremely important factor, as it could affect your ability to get insurance coverage for your boat. If your boat is currently insured and you’re considering a motor upgrade, make sure you know your insurance company’s rules for horsepower limits. If you upgrade without abiding by these rules and notifying your insurance company, there’s a good chance they won’t cover any claim you file.

Premium Cost

While abiding by your insurance company’s rules for boat horsepower, it’s important to remember that doesn’t mean a change in horsepower won’t bring a change in your premium cost. As a rule of thumb, boats with higher horsepower will be more expensive to cover.

Type of Policy

In addition to solely considering the horsepower of the boat, the overall size of the vessel, which takes horsepower into account, may determine the type of boat insurance policy you need to get. For example, your homeowner’s or renter’s insurance policy will usually cover smaller powerboats with less than 25 horsepower. Boats that are larger and have more than 25 miles per hour horsepower almost always require a separate boat insurance policy.

Dangers of Overpowering Your Boat

Bigger and faster is not always better. Putting more horsepower behind your boat may seem like an innocent way to add some excitement to your boating experience, but it could cost you a significant amount of money in fines, lawsuits and damage to your boat. Here are a few examples of how your need for speed can get you in trouble when it comes to boat maximum horsepower.

Breaking the Law

Is it illegal to overpower a boat? In some cases, yes. There are federal laws in place to ensure the appropriate horsepower limits are listed on all boats. State and local laws regarding overpowering your boat vary. Make sure you know the state and local laws for the areas in which you’ll be boating. Otherwise, your excess horsepower may be putting you at risk for fines and other consequences.

Accident Lawsuits

Even if your state and local laws don’t address overpowering your boat, you’re still putting yourself at risk in other ways. If you’re in an accident, the fact that your boat’s horsepower is above and beyond the manufacturer’s recommendations will be in the accident report. While you may not have fines because of breaking state and local laws, you are very susceptible to being found negligent and the victim of a lawsuit, especially in a case where there are damages.

Too Much Weight

In recent years, more horsepower hasn’t always meant more weight. However, it is still true in some cases, and that additional weight is another component of high horsepower that can be dangerous. For example, the additional weight can make a self-draining cockpit useless, leading to flooding problems.

Boat Damage

Even with additional horsepower that doesn’t add weight to the boat, the additional speed applies pressure that can cause significant damage to your boat. Every part of your boat, from the transom to the bow, was created to withstand a certain amount of pressure and stress. If you decide to ignore the boat’s maximum horsepower and overpower it, you’re exposing every part of your boat to pressure above and beyond what it was designed to endure, risking significant damage to the hull of your boat.

Finding a Boat With the Ideal Balance

As a boat manufacturer, at Formula Boats we know the balance of giving you the power and speed you want while making sure safety is a priority. If you’re considering purchasing a boat, our online boat builder gives you the opportunity to fully customize several different boat models with a few different horsepower options. You can be sure horsepower options for each boat model we provide are within the limits we believe maximize your performance while maintaining safety.

Discover a boat you like through our boat builder? We have dealers located throughout the country ready to help you find your boat. Get started by searching for the dealer location closest to you on our website.

Even though we narrow down the options, it can still be tough to choose the amount of horsepower that will give you performance based on boat weight and use, but also fuel efficiency. If you’re interested in one of our boat models, but are still wondering how much horsepower you need, we’re here to help — please don’t hesitate to contact us .

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Calculating Boat Fuel Consumption for Smart Boating

Efficiently managing fuel consumption is a critical skill for boaters, not only affecting the range of your vessel, but also impacting overall expenses. But unlike cars or trucks, calculating a boat’s fuel usage is more complex due to constantly shifting sea conditions.

In this comprehensive guide, we will dive into the intricacies of estimating and computing fuel consumption for boats, empowering you to make informed choices for an optimal boating experience.

Key Points for Fuel Consumption

Determining the amount of fuel your boat consumes holds several significant advantages:

Range Projection

Understanding your boat’s fuel economy–the amount of fuel needed per mile or nautical mile–helps anticipate the safe distance you can cover with a specific fuel capacity.

Cost Analysis

Calculating fuel usage offers valuable insights into operational costs, particularly when comparing different boats or marine engines for purchase.

Comparison Tool

Many boaters rely on fuel consumption charts or use boat tests as benchmarks for comparison. This allows for smarter decision-making when selecting a new boat or engine based on efficiency.

Due to the ever-changing nature of sea conditions, boat fuel efficiency is measured in gallons per hour (GPH). The metric used is pounds of fuel consumed per horsepower generated per hour, commonly referred to as ‘brake-specific fuel consumption.’

Keep in mind that gasoline weighs approximately 6.1 pounds per gallon, while diesel comes in at around 7.2 pounds per gallon.

The relentless hum of a well-tuned four-stroke gasoline engine can consume an impressive 0.50 pounds of fuel per hour for every unit of horsepower it churns out.

And let’s not forget the tireless diesel engine, which burns through 0.4 pounds of fuel per hour for each unit of horsepower it generates.

But be warned, these numbers only scratch the surface–factors like boat drag, sea conditions, and efficiency losses can greatly affect your fuel burn.

To navigate through this maze, use this formula to estimate your boat or engine’s fuel consumption:

GPH = (specific fuel consumption x HP) / Fuel Specific Weight

Gas = 6.1 lb. per gal

Diesel = 7.2 lb. per gal

The key to unlocking maximum horsepower lies in these formulas, optimized for the engine’s peak performance at wide-open throttle. But don’t be fooled–fuel consumption actually decreases during cruising speeds.

And with advanced electronic and direct fuel injection systems, efficiency is taken to a whole new level.

Unlocking Boating Performance

The roar of the boat motor and the number of miles it can go on a single gallon of fuel are crucial elements to consider while out on the water.

These two concepts, known as ‘boat motor pitch’ and ‘miles per gallon (MPG),’ hold the key to unlocking optimal boating performance. So pay attention, because your next adventure may depend on it.

Boat Motor Pitch

The pitch of a boat motor typically refers to the pitch of the boat’s propeller. The propeller pitch is the distance that the propeller would move in one revolution if it were moving through a solid, like a screw through wood. It’s measured in inches.

A higher pitch means the propeller is designed to move the boat further with each revolution, which can be efficient for speed but may reduce the engine’s revolutions per minute (RPM).

A lower pitch propeller will move the boat less distance per revolution but can increase RPM, potentially offering better acceleration and power for carrying heavy loads.

Choosing the right propeller pitch is crucial for optimal boat performance. It needs to be matched with the boat’s size, weight, and the motor’s power to ensure the engine operates within its recommended RPM range for peak efficiency.

Miles Per Gallon

MPG in the context of boats refers to the fuel efficiency of the boat. It indicates how many miles the boat can travel on one gallon of fuel.

Calculating MPG in boats is more complex than in cars due to variable factors like water conditions, boat weight, and hull design. A boat’s MPG can vary significantly based on these factors.

Higher MPG indicates better fuel efficiency, which is desirable for reducing fuel costs and environmental impact.

Boaters often look for ways to improve their MPG by optimizing the boat’s load, maintaining the engine, and using the boat at efficient speeds.

Assessing Fuel Usage and MPG

Begin by filling your boat’s tank to a precise level and recording the gallons added.

Then, set sail and take note of the distance traveled while considering sea conditions and cruising speed.

Upon return to the dock, refill the tank to the same level and record the additional gallons needed.

Using this information, you can determine the amount of fuel consumed during your trip and calculate your MPG using the formula: Distance Traveled / Gallons Consumed.

This equation is a valuable tool for determining the boat’s fuel efficiency and can be used to plan more efficient journeys in the future.

Many modern engines come equipped with gauges that display the total fuel consumption during a trip, as well as real-time updates on fuel efficiency to assist in saving fuel.

Maximizing Fuel Efficiency

The rumble of a boat motor is like a heartbeat to any avid boater. But did you know that how you trim your boat and manage fuel can make or break your entire experience on the water?

These two concepts are key players in maximizing performance and efficiency, leading you to smooth sailing and unforgettable adventures.

Boat Motor Trim

The trim of a boat motor refers to the angle of the outboard motor or stern drive in relation to the transom of the boat. Adjusting the trim changes the angle at which the hull meets the water.

Proper trimming can significantly affect the boat’s performance. When a boat is trimmed correctly, it runs more efficiently, achieving optimal speed and handling. The goal is to find the trim sweet spot where the boat planes smoothly on top of the water with minimal resistance.

Trimming the motor too low (in) causes the bow of the boat to sit lower in the water, increasing drag and reducing speed and efficiency. Trimming too high (out) can cause the propeller to ventilate, leading to loss of propulsion and potential engine damage.

Fuel Economy

Fuel economy in boating refers to how efficiently a boat uses fuel, typically measured in GPH or MPG.

Optimizing the trim of the boat can lead to better fuel economy. When a boat is properly trimmed, it reduces drag and allows the boat to move through the water with less effort and power. This efficiency translates into less fuel consumption for the distance traveled.

Additionally, a well-trimmed boat can also reduce engine strain and potentially extend the life of the motor.

Balancing Trim and Fuel Economy

Achieving the best fuel economy involves finding the optimal trim setting where the boat runs most efficiently. This setting varies depending on the boat’s design, load, water conditions, and speed.

Boaters often use trim tabs or power trim (adjustable with buttons or a lever on the throttle control) to adjust the trim level while underway, constantly fine-tuning for the best performance and fuel efficiency.

It’s important to monitor the boat’s performance indicators such as speed, RPM, and fuel consumption gauge, if available, to determine the most efficient trim setting.

Final Thoughts

Fuel up for success on the open seas by mastering your boat’s fuel consumption and miles per gallon. With this crucial knowledge, boaters can navigate their vessels with confidence and make informed decisions for efficient and cost-effective travels.

Don’t sail blindly–install a fuel monitoring system to track your consumption for ongoing management and worry-free long-distance cruises.

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How The Power Requirement Of A Ship Is Estimated?

One of the most important stages of a ship design process is the estimation, calculation and optimisation of a ship’s power requirements. Why? Because the power of a ship is a deciding factor for many other aspects of the industry- both the market and the environment.

A ship with more power requirements will automatically require larger amounts of fuel for each run of voyage, resulting in a hike in fuel expenses for the owner. Also, according to the recent trends, the overall efficiency of a ship is quantified by Energy Efficiency Design Index (EEDI) . The lesser the EEDI of a ship, more is the efficiency of the ship from an environmental and societal point of view. As the EEDI of a ship being proportional to the power required, it is always preferred by the designers to reduce the power requirements of a ship by every way possible. It reduces the EEDI, and in turn, brings down the carbon footprint of the ship.

Before we go into the core topic of this article, let me tell you what this article is about. In this article, we will first look at the ways of determining the power requirements for Marine Diesel Engines and Diesel Electric Propulsion Systems (note that the methods of estimating the power ratings for both the systems are quite different from each other). However different they may be, the first step is always the same, regardless of the type of propulsion system that is to be used by the ship, as discussed below.

The First Step: Calculate the Resistance of a Ship

In order to calculate the resistance of a ship, the first step is to conduct a towing tank test . In case of new hullforms , a towing tank test is preferred. However, if the hullform of the ship in design has already been tested in a tank, it is preferred to just follow the scaling method (Which we shall discuss soon).

In a towing tank test, the resistance of the model scale is obtained in the computer of the carriage. This is then scaled up to the ship’s scale by using a set of steps recommended by International Towing Tank Conference (ITTC).

The towing tank however gives on the bare hull resistance of the ship. Air Resistance, Resistance due to Appendages and a Correlation Allowance are added to obtain the Total Resistance of the ship . This total resistance when multiplied with the ship’s velocity gives the Effective Power of the ship (P E ).

An Interesting Tip: If you now rate the ship’s engines to the obtained effective power, the ship should move at the design speed. Right? But if you actually did, the ship would only be able to operate at a speed lower than this. We will discuss the reason as we proceed.

The Second Step: Decide on the Type of Ship Propulsion System

This is one of the most deciding steps of the entire process. Selection of the wrong type of propulsion system may result in an economic catastrophe for the ship in future. Years of experience and research has now provided us with a clear idea as to what kind of propulsion should be preferred on different kind of ships.

Diesel-Mechanical Propulsion is preferred in most cargo ships which require low speed operations and lower operating costs (operation costs for Heavy Fuel Oil used in Marine Diesel Engines is lesser than operating costs of Diesel Electric Propulsion Systems). In the recent times, slow steaming has become an efficient method to counter the effects of the maritime recession, and diesel propulsion is hence preferred in most cargo ships (bulk carriers, oil tankers, container ships).

Diesel Electric Propulsion is preferred in ships which require more electric power (for example cruise ships require more electric power to run its facilities, drillships that require dynamic positioning systems for most of the time of operation, etc.) and ships that require undisturbed operations with varied torque (for example, tugs). This is one of the most notable advantage of diesel electric propulsion. Where diesel mechanical propulsion systems do not offer high efficiencies at all torques, diesel electric propulsion systems can operate at high efficiencies at almost all torque variations.

In the above graph, it is evident that the torque supplied by the Engine (diesel engine) varies with speed. That is, higher torque can only be obtained at higher operating speeds. But if higher torques (of propeller) are required at lower speeds (which is the case of tugs and dynamic positioning systems), an electric motor (which is used in diesel electric propulsion systems) stands out.

The Third Step: Estimate the Engine or Diesel Alternator Ratings

For Diesel Mechanical Propulsion:

Remember the question we had raised in the tip above? Why would the ship not operate at design speed if we rated the engines at the effective power?

> The resistance calculated from the towing tank tests is only the bare hull resistance, that is, the effect of the propeller is not considered in the above. Whereas, when a propeller operates behind the ship, there is the following we must consider here:

Resistance of the ship increases from the value calculated in bare hull condition. The propeller must operate at a torque that is sufficient to overcome this augment in resistance and also enable the ship to overcome its bare hull resistance.

Hence, due to the losses in the propeller, the power delivered to the propeller (P D ) at the shaft output should be more than the effective power (P E ). The ratio of the effective power to the delivered power is called Quasi Propulsive Coefficient (QPC). QPC usually ranges from 0.55 to 0.65.

> The power at the engine output (i.e. shaft input) is not fully obtained at the shaft output. This is because of the frictional and heat losses that occur along the length of the shaft. These are termed as shaft losses. Shaft losses are usually taken as 2 percent.

> In case of smaller ships where high rpm engines are generally used, reduction gearboxes are used to reduce the shaft rpm, or operated at various RPMs. The losses induced by the gearbox are classified under gearbox losses. Gearbox losses range from 4 to 5 percent.

> The resistance estimated during the design phase does not consider the effect of waves. Due to the action of waves, the actual resistance on a ship is higher than that in calm water conditions. Hence, a margin of 15 percent is considered as sea margin, and the engine power is rated so that it overcomes the sea margin.

> It is always desirable to keep specific fuel oil consumption as low as possible . For marine diesel engines, the Specific Fuel Oil Consumption (SFOC) is minimum when the RPM of the engine is corresponding to 85% of maximum continuous rating (MCR). Which means, that the design speed should be attained, not at the rated MCR but at 85% of the MCR. So to obtain the MCR, the corresponding factor of 0.85 is considered.

The following table shows a calculation that is used to obtain the rated engine power from the effective power of twin-engine ship using the above factors:

For Diesel-Electric Propulsion:

I will discuss the basic components of a diesel electric propulsion just to an extent that makes is possible for a reader at a preliminary stage to understand what we will be discussing on the estimation of power rating of a diesel electric propulsion system.

The basic components of a diesel electric propulsion system are:

Diesel Generators, Transformers, Electric Motors and Loads. Now, the loads on the system may be a electric motor driven propulsion pod, or a bow thruster, or any component of hotel load (lighting, HVAC, etc.)

In this case, the electric propulsion motors, propellers and other loads together form the load of the entire power plant. But it is to be considered that not all loads will be in operation in every condition. For example,

In harbour, the propulsion loads will be absent, whereas the hotel loads will be present.

In case of Dynamic Positioning Operations, both hotel loads and propulsion units will be in operation. So in this case, the load on the diesel generators will be maximum.

So, we will basically need to calculate the total power requirement before deciding upon the number of diesel generators required to meet all the conditions. Once the total power is decided, the number of diesel generators will be decided upon based on certain principles that we shall discuss later on.

First, in order to calculate the total power requirement, designers prepare a Load Chart which lists out all the electrical loads on the ship. And the load chart is prepared, taking into consideration three operating conditions in general:

Sailing, Harbour and Maneuvering.

In the load chart, the power requirements of each electrical load on the ship is calculated by multiplying the Maximum Rated Power of the component with two factors:

Load Factor: It is the ratio of the operating power to the maximum power rating of the component.

Utility Factor: It is a factor which determines the extent of operation of the particular component in a particular condition.

For example, for a steering gear equipment:

Note that the utility factor is 0.8 in Sailing and Maneuvering Conditions , but 0 in Harbour condition, since in harbour condition the steering gear is not used. So the contribution of the steering gear equipment to the total power requirement in Sailing Condition will be zero.

In the similar manner as illustrated above, the load chart is prepared for all the electrical components on the ship. A sample of the same would look like the following:

Once the load chart is prepared, the total power requirement for each of the three conditions (Sailing, Harbour and Maneuvering) are calculated by adding up the power requirement for each component for each of the conditions (follow figure 4). Once this is clear, we will now refer to Figure 4 to understand how the total number of diesel generators is decided.

The two rules to be followed in deciding upon the number of generators are:

If more than one generator is operating in any condition, both the generators should share equal amount of load.
The load on each generator in any of the three conditions should not be more than 70 percent of the rated power of the generator. (Or, the maximum rating of each generator is decided based upon the condition that seventy percent of the maximum rating is more than the load on the generator in any of the three conditions)
One additional generator should always be included, which is for standby purpose. Note that this standby generator will not share the load in any of the above three conditions unless any of the working generators are out of order. So the standby generator is not included in the above calculation, but it is usually of the same rating as of the other generators.

This process is iterated by varying power ratings and varying number of generators until the above first two conditions are satisfied, and a situation similar to the one in Figure 4 is obtained. It is advised that you analyse the first two conditions using the above figure to understand it in first hand.

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About Author

Soumya is pursuing Naval Architecture and Ocean Engineering at IMU, Visakhapatnam, India. Passionate about marine design, he believes in the importance of sharing maritime technical knowhow among industry personnel and students. He is also the Co-Founder and Editor-in-Chief of Learn Ship Design- A Student Initiative.

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Dear Soumya, It was a pleasure to read about the power requirements. I am a Master Mariner and run a Maritime Academy in Kolkata and recently completed a course on Naval Architecture. I have desisigned a fiberglass 40 ft fishing trawler and would like to use in the ganges estuary with a 100 hp marine diesel engine with a chinese gear box. what would by the advantages if I were to go for motor propulsion run by generator with one stand by and during trawling both generators could be used for more power.

Dear Capt. Arnab,

It would actually depend on the kind of operation the vessel is meant for. In case of trawling operations, there is usually a requirement of high torque at low speed regions, which would make it advantageous to go for DG powered motor propulsion. You however need to compare the calculations done for both cases, i.e. for MDE and Electric Propulsion. Based on the efficiency achieved from each, the suitable propulsion system can be chosen.

Can you explain how you got the numbers from figure 4? Thank you:)

Kindly throw some light on Fig 4 findings.

Will appreciate same.

Dear soumya, I am Aman Chouhan I have to submit a paper on diesel engine matching and selection for naval platforms . Could you please help me regarding this topic . if you can send some paper related to this

Why are all the load factors in Figure 3 set as 0.8?

Thanks, Kayla

what values would i be looking for if I wanted to calculate the total energy input of a ship? Trying to write a report on Analysis of Energy and Exergy Systems in a selected vessel.

Thanks for your work!

Dear Soumya,

I sincerely appreciate your work, but I’m really new to marine engineering. Please, could you please explain how to calculate the electrical requirement of a chemical tanker in different modes. I truly appreciate, thank you.

Dear Soumya, i sincerely appreciate for what valuable work you are doing and sharing with everybody. i am very curious to now how to begin to design the electrical power requirement for a ship. and what considerations must be take in to account while designing.

Thanks, Samson Adam

Thanks for this great summary of the current design process. However many companies are now relying on cfd calculation (Star-ccm+ for example) instead of towing tank tests. Also for all the assumptions made for the rest of the propulsion system, many shipyards and architects now use system simulation (Amesim for example). These bring much more accurate results and innovative propulsion solutions!

@Romain: Thank you for the input.

i have a query …

what power factor to be assumed on sockets for feeding shore power to boats

Hi anybody can help me about IEC standards for ship power balance computations..Need it badly thank you very much

Hi anybody can help me about IEC standards for ship power balance computations..Need it badly thank you very much for techinical engineering report study..thank you

Has Anybody evaluated deck mounted containerised generator sets, for electric propulsion, please?

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IMAGES

How to calculate yacht fuel cost
Power consumption yacht: on-board battery management and charging
Boat Electrics; How to Calculate Your Daily Amp Requirement
Power Yachts & Rates
Power Yachts & Rates
MJM Yachts: The World's Most Fuel Efficient Powerboats

COMMENTS

Boat Electrics; How to Calculate Your Daily Amp Requirement
The relationship between power and current is expressed as: Power (W) = Current (A) x System Voltage (V) To derive amps from watts, simply transpose this equation and divide the wattage by the system voltage. For example, a 6 watt navigation light bulb in a 12 volt system will draw 0.5 amps - which, if it's switched for ten hour each day when ...
Daily Current Draw Calculator
Daily Current Draw Calculator. The Daily Current Draw Calculator Calculation Sheet has intentionally been left unlocked in order that you may enter the current draw of each of the appliances on your boat, together with the daily periods that you have them turned on. Current draw: The appliance amps currently entered on the sheet are notional.
PDF Vessile_Energy_Usage_Estimator.xlsx
The worksheet will automatically calculate the total amp hours for each condition while on board the boat allowing you to determine the energy usage for your vessel. With this information at hand, you can confidently size the battery bank and renewable energy equipment needed to support your live aboard lifestyle.
Marine Power Usage
Marine Power Usage The chart below shows examples of energy consumption of various equipment. The current (amps) is multiplied times the amount of hours per day is used to determine the Amp Hours per day of energy that is consumed. These values are based on a 12 V DC nominal system.
Fuel consumption calculator
Fuel consumption calculator - MerCruiser - Cummins MerCruiser - Crusader - Volvo Penta Diesel - Mercury - Evinrude - Honda Marine - Yamaha Marine - Suzuki Marine - Tohatsu - Johnson - Outboards | GPH MPG LPH KPL
How to improve power management on a yacht
A standard 'off the shelf' mid-size production boat is likely to be fitted with a 60A battery charger which is used by the boat's generator, if it has one, or when shore power is plugged in. The engine will also have an alternator which will typically produce between 35 and 60A of charge, depending on the size of the engine.
How To Calculate Amp Usage Aboard a Boat
How To Calculate Amp Usage Aboard a Boat Almost every cruising boat, including us, seems to underestimate the amount of electricity we use per day when planning alternative energy - for us solar panels and wind generator. Very frustrating when your goal is to live by the sun and wind and not have to run the diesel or generator daily!
Electrical needs and power consumption on a sailboat
To determine the power consumption on our sailboat, we've compiled an energy balance excel sheet with all the electrical devices we have on board. Devices that continuously run, like the fridge or water system, Variable devices on 12V that need to run during the day, the night or while sailing and long passages.
Power Consumption Calculator
All I have developed a spread sheet to calculate the power consumption of my Jeanneau 39i whilst cruising the med underway and at anchor. I built it to estimate how often I would n
How Much Power Do You Need For A Passage?
On my boat, I've found that my power consumption might even double on passage, although it depends on the conditions I encounter. All boats have different energy requirements, but if you understand that your power use may greatly increase during an extended passage, you can monitor your batteries closely and keep them from running low.
Simple Guide for Calculating Your Sailboat's Energy Budget
After spending way too much time figuring out how to size the power system for our boat, I thought it would be good to create a simple guide to estimating your needs. It is an excel file you can download/modify with your own sailing or RV needs. I ran through this math with our teardrop trailer, and now with the more complicated sailboat. This whole file is set up for a 12-volt system, you may ...
Autopilot Power Consumption
In this case it is easier to figure an average power consumption equal to half the peak power rating of the drive motor for the 24 hour calculation for a "bad case" of power consumption. You will then be well under 360 Amp-hours for 24 hours. We have the ST6000 on our boat, which I'm not on at the moment.
Managing your boat s power consumption
All this technology makes operating a boat easier and safer, but the advances also call for more robust electrical components and systems to handle the power consumption — a fact some boat owners overlook, according to marine electrical system experts.
Sailo Boat Calculator
The calculator is organized in multiple tabs that show costs breakdown and allow for detailed customization. For example, the fuel cost tab computes fuel consumption based on the type and size of your boat, estimated HP, and average current gas prices. To make this calculation more accurate you can enter a more exact fuel consumption for your boat and more accurate local gas prices.
DC Load calculations for marine and mobile projects
ABYC Standard E11 proposes a way to do DC load calculations for boats. The results of the basic load calculation can be used to determine the amp rating for switch panels. The data collected can then be used to calculate daily power consumption and ultimately the results can be used as a way of calculating battery size. The first part of the ...
Boat Speed Calculator
The boat speed calculator determines the top speed of a boat based on the boat's power and displacement. If you wonder how fast a boat can go, this calculator will help you answer that. The calculator also utilizes a constant known as Crouch constant which differs based on the type of the boat.
Fuel Calculator
Welcome to the West Nautical Fuel Calculator. HOW TO USE: To plot points on the map, click with your mouse - this will automatically update the distance table. Then enter the speed, fuel consumption, and fuel cost to determine the total cost of the trip. Example 1: A fast 30m yacht cruising at 20 knots ( Lady Amanda) will consume roughly 400 ...
Crouch's Calculator
Crouch's Calculator. The calculated value is indicated by the shaded heading in the table. This useful calculator computes an estimate of boat speed for a modern planing monohull using inputs of the power at the propeller shaft, the total boat weight, and a coefficient called the hull factor. The calculator can also compute any one parameter ...
Boat Fuel Consumption Calculator
Enter the specific fuel consumption, horsepower, and fuel-specific weight into the calculator to determine the boat fuel consumption.
How Much Horsepower Do I Need for My Boat?
There are several factors to take into consideration when you're determining how much horsepower you need — the manufacturer's limits and recommendations, boat horsepower-to-weight ratio, fuel efficiency, use of the boat, number of people on the boat and an industry rule of thumb.
Calculating Boat Fuel Consumption for Smart Boating
Calculating Boat Fuel Consumption for Smart Boating Efficiently managing fuel consumption is a critical skill for boaters, not only affecting the range of your vessel, but also impacting overall expenses. But unlike cars or trucks, calculating a boat's fuel usage is more complex due to constantly shifting sea conditions.
How The Power Requirement Of A Ship Is Estimated?
How The Power Requirement Of A Ship Is Estimated? One of the most important stages of a ship design process is the estimation, calculation and optimisation of a ship's power requirements. Why? Because the power of a ship is a deciding factor for many other aspects of the industry- both the market and the environment.